You can aquire a no-CD crack/patch to play the game without your CD on battle.net or LAN. (Does this work with single player?)
If unable to find a no-CD patch you can always rip an ISO image of the disc and mount it on a virtual CD-Rom drive.
It's also impossible to play on battle.net without a valid CDKey, and I'm not sure if it's possible to bypass the CDKey check on installation.
Check one of the stickied threads which I believe has a link to a no-CD crack.